Abnormal, excessive startle is a feature of three distinct conditions: hyperekplexia or startle disease, jumping (the jumping Frenchmen of Maine), and startle epilepsy. The mechanisms of normal / startle and startle epilepsy are reviewed by Brown et al. (this volume).
Kirstein and Silverskiold (1958), first described startle disease. Two sisters, their father, and the daughter of one of the sisters suffered from sudden violent falls precipitated by stress, fright, or surprise. Three of these family members also had nocturnal myoclonus. The authors cautiously considered the disorder to represent an unusual, genetically determined form of drop seizures. In a letter to Lancet, Kok and Bruyn (1962), drew attention to a hereditary disease affecting 29 individuals in six generations of a German–Dutch family with 127 members. Suhren et al. (1966), described this family in much greater detail. The affected individuals had a strikingly excessive response to startle elicited by visual, auditory, and proprioceptive stimuli that failed to produce a response in most normal individuals. These authors coined the term hyperekplexia, i.e. excessive jerking to describe the condition.
The disorder occurs in two forms: a minor form in which the response is quantitatively different from normal, i.e. the startle response is more violent; and a major form in which there are also additional clinical symptoms. In the major form, patients, when startled, experience momentary generalized muscular stiffness with loss of voluntary postural control causing them to fall as if frozen, with their arms at their sides, unable to carry out protective movements.